This invention relates to the field of polymer blends, or alloys, and more particularly, to hydrophilic blends of polyvinylbutyral (PVB) and poly(N-vinyl lactam) and to the use of these blends in a variety of applications including the formulation of lubricious coating compositions.
There has long been a need in the art for lubricious materials which are non-slippery when dry but exhibit lubricious or slippery properties when contacted with aqueous fluids. Applications for such materials are numerous and diverse and include fabrication into surface coatings, foams, fibers, films, or solid articles which absorb water, impart wettability or reduce the coefficient of friction in aqueous environments. Uses include but limited to, coatings for catheters, condoms, invasive devices and test probes which are lubricious only when wet, antifog coatings for lenses, windows, etc., drag reducing coatings for ships, burn and wound dressings, contact lenses, antistatic coatings, hydrophilic fibers and matrices for controlled release of pharmaceuticals, dyes, fragrances, salts and the like. It had previously been proposed to reduce the coefficients of friction of these and similar devices and materials by the use of non-permanent coatings of silicone or certain fluorocarbons, neither of which are hydrophilic, and which do not have as low coefficients of friction as are necessary or desirable for some applications. The fluorocarbon coatings also have the disadvantage of being difficult to handle because they are always slippery, not just when slipperiness is desired.
Coatings and articles useful for insertion into the body, for example, are described in U.S. Pat. Nos. 4,100,309 and 4,119,094. Articles such as catheters and condoms described in these patents are obtained by coating a suitable substrate with a polyvinylpyrrolidone-polyurethane interpolymer. The coatings are obtained by using a solution of isocyanate containing prepolymer and polyurethane, with a solution of polyvinylpyrrolidone. The isocyanate can be modified with chain extenders (diols, etc.) which effectively produce a high molecular weight polyurethane in situ. The requirement that reactive isocyanates be present introduces unavoidable chemical instability (pot life) and eliminates the possibility of utilizing aqueous or alcoholic solvents for preparation. Isocyanates will also react with and inactivate many desirable additives such as pharmaceuticals, surfactants and dyes.
U.S. Pat. Nos. 4,373,009 and 4,472,467 describe similar compositions. These patents, however, require a chemical reaction forming a covalent bond between isocyanates and active hydrogen groups reactive toward isocyanate on the vinyl lactam or ethylene oxide polymers to produce the objects of the invention. These patents actually teach away from the use of chemically inert components.
U.S. Pat. No. 4,642,267 describes hydrophilic blends of polyvinylpyrrolidone and linear preformed polyurethanes which afford low friction surfaces when wet. Limiting the hydrophobic component to polyurethanes restricts the utility of such alloys in certain applications, in particular where concerns of low cost, hydrolysis stability and food packaging regulations are paramount.
Polyvinylpyrrolidone, a commercially available poly (N-vinyl) lactam, is a well known hydrophilic, polymer having numerous applications including being a film former, protective colloid and suspending agent, dye-receptive resin, binder and stabilizer, physiologically acceptable polymer, etc. However, being water soluble, polyvinylpyrrolidone and related poly (N-vinyl) lactams will eventually be leached from coating compositions and other materials formulated with the polymer when contacted with aqueous fluids. Thus, the practical value of known compositions containing polyvinylpyrrolidone as lubricious coatings, other than the compositions claimed in U.S. Pat. Nos. 4,100,309, 4,119,094, 4,642,267 and others cited above, is greatly limited due to the erosion of their lubricious properties as the polyvinylpyrrolidone component dissolves or is leached into the surroundings aqueous medium.
The Handbook of Water Soluble Gums and Resins (McGraw-Hill, 1980) lists many polymers which form "compatible" solvent blends with PVP, including polyvinylbutyral. However, no mention is made of any unexpected insolubility resulting from such combination, nor are any friction-reducing properties described. In fact, the solvent combination appears to be critical to the preparation of homogeneous coatings with useful properties.